D-Geo PiPeline

Design of pipeline installation

Pipelines are an important part of the underground

infrastructure. They are the lifelines of our modern

society. The successful operation of a pipeline

system on the long term, however, is largely

determined by the quality of the engineering works

prior to the installation of the pipeline.

From time immemorial, pipelines have been

installed in trenches. After excavation of the trench

the pipeline is installed on the bottom of the trench

and is subsequently covered by the excavated

soil. Since the 1970s, Deltares (formerly known as

GeoDelft) has been involved in the development

and execution of trenchless technologies.

Trenchless techniques provide a logical alternative

when pipelines need to cross roads, railways,

dikes, wetlands, rivers and other structures that

have to remain intact. These techniques minimize

the impact of installation activities in densely

populated and economically sensitive areas.

Previous releases of D-Geo PiPeline were named

MDrill. MDrill was one of the first design codes for

Horizontal Directional Drilling (HDD). MDrill was

the result of years of research. Since the release

of the first version in 1995, the design code has

regularly been updated with new knowledge.

Recently, two modules have been added to take

into account the installation of pipelines using

micro tunnelling and the installation of pipelines

in trenches.

General

The program D-Geo PiPeline provides tools for the design of a pipeline

installation in a trench and trenchless installation, using the micro

tunnelling technique or the Horizontal Directional Drilling (HDD)

technique. D-Geo PiPeline allows the user to minimize the risks

during and after installation.

• Geometry and 3D pipeline configuration

The graphical user interface allows an easy and fast input of the

soil layers. The upper soil layers can be designated as load for

settlement calculation purposes. The three dimensional pipeline

configuration can be entered by a fast tabular input.

• Arching

In case of trenchless installation, D-Geo PiPeline applies a reduced

neutral soil load to incorporate the effect of arching. The amount

of reduction depends on the installation method, the depth of the

pipeline, diameter and the soil properties.

• Pipe stress analysis for horizontal directional drilling

installation

D-Geo PiPeline calculates the stresses in the pipeline during the

installation stages in both axial and tangential direction. In

a comprehensive report a stress verification is given for each

pipeline material used.

• Advanced calculation of settlements

Vertical displacement of soil below the pipeline that occurs after

installation is an important factor in assessing the stresses in

the pipeline. Pipeline settlement may be entered manually if the

vertical settlements are available. For more accurate results,

D-Geo PiPeline can use the D-Settlement computer program

without additional input.

D-Geo PiPelineDesign of pipeline installation

2D cross section

• Advanced pipeline stress analysis

For advanced pipe stress analyses special programs need to be

used. These programs need an advanced set of soil mechanical

parameters, provided by D–Geo Pipeline. The programs will

generate a complete spring model around the pipeline for

further analyses. The soil mechanical parameters provided by

D-Geo PiPeline are:

• neutral, passive and reduced vertical soil load

• vertical and horizontal modulus of sub grade reaction

• ultimate vertical and horizontal bearing capacity

• neutral horizontal soil load

• vertical displacement

• maximum axial friction

• friction displacement.

D-Geo PiPeline comes as a standard module, which can be extended

further with other modules to fit two other applications related to

pipeline installation:

• D-Geo PiPeline Standard module (Horizontal Directional Drilling)

• Micro Tunnelling module

• Trench module.

Standard module (Horizontal Directional Drilling)

D-Geo PiPeline enables the fast design of a pipeline configuration,

installed using the Horizontal Directional Drilling (HDD) technique.

In HDD three installation stages are considered: Pilot drilling;

reaming the initial pilot borehole and pulling back the pipeline.

The initial borehole is called a pilot hole. The diameter of this pilot

hole is enlarged using a reamer. Depending on the required final

borehole diameter, the borehole can be enlarged in several steps

using reamers of increasing diameters. Finally, the pipeline is

pulled into the borehole.

Features

• Advanced input of the ground water pressure distribution.

• Drained and undrained behaviour of soil layers.

• Graphical output of calculated drilling fluid pressures.

• Library with steel and polyethylene pipelines.

• Standard calculation scheme for bundled pipelines.

• Calculation of settlement of the soil layers below the pipeline.

• Standard pipe stress analysis.

Drilling fluid pressures

The minimal required drilling fluid pressure is the pressure necessary

for an effective return flow, capable of transporting cut soil particles

towards the surface. The upper boundary of the allowable drilling

fluid pressure indicates the pressure at which a blow-out is likely to

occur. The lower boundary indicates the pressure at which fractures

around the borehole are expected. Both minimum and maximum

allowable drilling fluid pressure depend on depth and soil properties.

Drilling fluid pressures are calculated along the entire borehole and

visualized in a graph showing both the upper and lower boundary.

Drilling fluid pressures can be calculated for all installation stages

(pilot, reaming and pull back).

Pipeline material

D-Geo PiPeline is capable of dealing with pipelines made of different

materials. For steel and polyethylene a database containing

the material data is available. The database enables a quick

re-calculation for alternative material types and dimensions.

Pull back force calculation

D-Geo PiPeline calculates the pulling force on the pipeline that is

required to pull the pipeline into the prereamed borehole. The pull

back force is based on buoyancy control and consideration of the

soil-pipeline interaction in the bends of the drilling line.

Barrel reamer and Fly cutter

Drilling fluid graph

Pipeline stress analysis

Soil mechanical parameters are used for a pipeline stress analysis.

The standard pipeline stress analysis by D–Geo PiPeline is based on a

limited set of parameters. D-Geo PiPeline calculates the stresses in the

pipeline during the installation stages in both axial and tangential

direction. In a comprehensive report a stress verification is given for

each pipeline material used. The calculated stresses are compared

with the allowable stresses according the Dutch pipeline code (NEN

3650). The pipeline stress report contains:

• used input data

• calculated axial, tangential and combined stresses for all

installation stages

• verification of the pipe stresses

• check on pipeline deflection

• check on implosion for polyethylene pipelines.

Micro Tunnelling module

Micro tunnelling is the technique which uses a tunnelling machine

to remove the soil. Micro tunnelling usually starts horizontal at

a certain level below the surface. Start and reception shafts are

created for the micro tunnelling machine. In the start shaft a jacking

frame and micro tunnelling machine are installed in front of the pipe

sections. The jacks push the pipe elements section by section ahead

towards the reception shaft. As the length of the advancing micro

tunnel increases, the friction forces will increase. Lubrication fluid

may be applied to reduce the friction. Very often, drilling fluid is

used for soil removal and face stabilization at the front of the micro

tunnelling machine.

Features

• Drained and undrained behaviour of soil layers.

• Graphical output of calculated face support pressures, trust forces

and subsidence through.

• Calculation of settlement of the soil layers below the pipeline.

Face support pressures

The micro tunnelling machine changes the stress conditions in the

soil. The deviations from the original stress conditions are largely

determined by the size of the overcut and the applied shield. Small

deviations from the original conditions are acceptable as long

as the stability of soil adjacent to the micro tunnelling machine

is maintained. A relatively low face support pressure may lead to

collapse in front of the shield, which in turn may lead to subsidence

of the surface or to settlement of soil layers below a construction or

pipeline. A relatively high face support pressure can lead to a blow

out of drilling fluid or may lead to surface heave.

While drilling, the shield pressures have to be kept between certain

limits. To prevent the possibility of collapse of the soil in front of the

micro tunnelling shield, causing subsidence, the soil at the front is

kept stable by maintaining a minimal face pressure. Depending on

the soil type the minimal support pressure can be calculated using

Jansecez and Steiner theory, or Broms and Bennermark theory. A

maximum support pressure should not be exceeded to prevent

uplift of the soil above the micro tunnelling machine or a blow out

of drilling fluid towards the surface. The support pressure, the target

pressure during drilling, should be in between the two limits. At the

neutral pressure, the face support pressure is in equilibrium with the

current horizontal soil pressure.

Thrust force

The micro tunnelling machine is at the front of the advancing pipe

sections. As the length of the advancing micro tunnel increases,

the friction forces along the micro tunnelling machine and the pipe

segments rises. Lubrication fluid may be applied to reduce the

friction. D-Geo PiPeline compares the predicted thrust force with the

maximum allowable thrust force.

Surface subsidence

During the micro tunnelling drilling process the volume of removed

soil is generally larger than the volume of the micro tunnel or

pipeline (overcut). The volume difference will lead to soil movement Hydraulic jacks in the start shaft

Maximum, neutral and minimum face support pressure

Drilling fluid graph

towards the borehole, which in turn will lead to surface subsidence.

The magnitude of the subsidence (trough) is calculated and

graphically shown by D-Geo PiPeline.

Trench module

The majority of the underground pipelines are installed in a trench.

After excavation of the trench the pipeline is installed at the bottom

of the trench and subsequently covered by the excavated soil. The

interaction between the pipe and the condition of the soil material,

which is placed back in the trench plays an important role in the

engineering of the pipe. The compaction of the fill leads to differential

settlement of the fill above the pipe and adjacent to the pipe.

Features

• Upheaval and uplift check.

• Graphical output of the calculated uplift safety factor; upheaval

safety.

• Calculation of settlement of the soil layers below the pipeline.

Uplift safety

Pipeline installation in wet soft soil environments may lead to

buoyant behaviour of the pipeline. In case of superficial installation

the soil cover above the pipeline may be insufficient to withstand

the buoyant force of an empty pipeline. D-Geo PiPeline provides an

Uplift check and Uplift safety factor chart.

Interaction with other Deltares systems tools

D-Geo PiPeline interacts with other Deltares systems tools for

settlement analysis, seepage analyses, central project and

database storage:

• D-Settlement for analyses and import of settled geometry

• D-Geo Stability for slope stability analysis

• Scia PiPeline for advanced structural analysis of pipeline behaviour.

Support

Deltares systems tools are supported by Deltares. A group of

70 people in software development ensures continuous research

and development. Support is provided by the developers and if

necessary by the appropriate Deltares experts. These experts can

provide consultancy backup as well.

On-line software (VMware)

All popular geotechnical Deltares simulation products are available

over the internet via our Online Software service (Software as

a Service (SaaS)). An internet connection and subscription is

sufficient for worldwide access. Billing is according to the actual

use and subscription costs per quarter.

Installation of a pipeline into a trench

Uplift safety factor chart

Subsidence trough

PO Box 1772600 MH DelftBoussinesqweg 12629 HV DelftThe Netherlands

T +31 (0)88 335 81 88software@deltares.nlwww.deltares.nl/softwareonlinesoftware.deltares.nl

Uplift safety factor chart